Fine clock resolution digital phase locked loop apparatus

ABSTRACT

A digital phase locked loop apparatus includes an input signal time detecting device that detects a phase of an input signal with prescribed time resolution obtained by dividing a cycle of an operation clock generated by a clock generator at a prescribed time. An output clock generating device outputs output clock time data per the one cycle in accordance with frequency control data. The output clock time data has a value corresponding to a phase of a virtual output clock generated by dividing the operation clock in accordance with the time resolution. A phase difference detecting device detects a difference between phases of the input signal and the virtual output clock, and outputs a phase difference signal in accordance with the detection result. The frequency control device changes the frequency control data in accordance with the phase difference signal.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. § 119 to JapanesePatent Application No. 2005-038890 filed on Feb. 16, 2005, the entirecontents of which are hereby incorporated by reference.

COPYRIGHT NOTICE

A portion of the disclosure of this patent document contains material,which is subject to copyright protection. The copyright owner has noobjection to the facsimile reproduction by anyone of the patent documentor the patent disclosure, as it appears in the Patent and TrademarkOffice patent file or records, but otherwise reserves all copyrightrights whatsoever.

BACKGROUND OF THE INVENTION

1. Technical Field

This invention relates to a digital phase locked loop apparatusincluding a phase locked loop circuit, which generates a reproductionclock in synchronism with reproduction data of an optical disc apparatusor a magnetic disc apparatus, as well as a recordation clock insynchronism with a wobble signal of the optical disc apparatus.

2. Discussion of the Background Art

A phase synchronization loop circuit (a phase locked loop circuit) isutilized in a data reproducing apparatus that reproduces data from arotational storage medium, such as an optical disc, a magnetic disc,etc., to obtain a clock that synchronizes with reproduction data. Thephase locked loop circuit is almost realized by an analog circuit thatemploys a voltage-controlled oscillator. However, a self-runningfrequency of such an analog voltage controlled oscillator tends to varyin accordance with a change in environment temperature or power supplyvoltage, thereby resulting in a long pull-in time of the phase lockedloop circuit. Then, a digital phase locked loop circuit has beenproposed as discussed in Japanese Patent Application Laid Open No.60.245312.

Since the digital phase locked loop circuit does not employ an analogvoltage controlled oscillator, the above-mentioned variation does notoccur, and a self-running frequency is stable with a frequency clockprecision (i.e., crystal precision) provided as a reference. Further,since being entirely configured by a digital circuit, the digital phaselocked loop circuit can be easily mounted on an integrated circuit,thereby an apparatus can be downsized and is low cost.

FIG. 25 is a block diagram illustrating an exemplary configuration of aconventional digital phase locked loop circuit. FIG. 26 illustrates anoperational wave appearing in the digital phase locked loop circuit ofFIG. 25. The digital phase locked loop circuit includes a phasecomparator 700, a counter 701, an incrementer-decrementer 702, and adivider 703.

The digital phase locked loop circuit needs a high frequency clock as anoperational clock PC2 used in the phase locked loop when time resolutionof a phase of an output clock FS thereof is to be enhanced. For example,a frequency of thirty-two times of a reproduction data rate is requiredas an operational clock in the digital phase locked loop circuit whentime resolution of an output clock phase of the digital phase lockedloop is to be thirty-two times of the reproduction data rate.

However, recordation and reproduction speeds for a CD and a DVD havesignificantly increased, and recently, the internal operational clockfrequency has become extraordinarily high in the above-mentionedconventional digital phase locked loop circuit.

As a result, it exceeds an operation frequency limit for the circuit,thereby the digital phase locked loop circuit becomes inoperative whenthe reproduction data rate is large. This invention is made in view ofthe above-mentioned aspects, and it is an object of the invention toachieve a fine time resolution of an output clock phase while using arelatively low frequency of an operational clock.

BRIEF SUMMARY OF THE INVENTION

Accordingly, an object of the present invention is to address andresolve such and other problems and provide a new digital phase lockedloop apparatus. The new and novel digital phase locked loop apparatusincludes an input signal time detecting device (2) that detects a phaseof an input signal (S1) with prescribed time resolution obtained bydividing a cycle of an operation clock generated by a clock generator ata prescribed time (N). The input signal time detecting device (2)outputs input signal time data (S2) in accordance with the detectionresult per the one cycle. An output clock generating device (5) outputsoutput clock time data (S5) per the one cycle in accordance withfrequency control data. The output clock time data has a valuecorresponding to a phase of a virtual output clock generated by dividingthe operation clock in accordance with the time resolution. A phasedifference detecting device (3) detects a difference between phases ofthe input signal and the virtual output clock, and outputs a phasedifference signal (S3) in accordance with the detection result. Thefrequency control device (4) changes the frequency control data (S4) inaccordance with the phase difference signal (S3).

In another embodiment, the clock generator generates a multi phase clockincluding a plurality of phase clock signals having different phases bya scale of time resolution per one cycle.

In yet another embodiment, the output clock generating device (5) isoperated by a clock of the one cycle and stores a state in accordancewith a phase of the virtual output clock. The output clock generatingdevice (5) determines the next state based on a relation between thefrequency control data and a current state. The output clock generatingdevice (5) outputs output clock time data in accordance with the nextstate.

In yet another embodiment, the output clock generating device (5) isoperated by a clock of the one cycle and including a plurality ofstorage devices to store a current state and one or more past states inaccordance with a phase of the virtual output clock. The output clockgenerating device (5) determines the next state based on a relationbetween the frequency control data, a current state, and the one or morepast states. The output clock generating device (5) outputs output clocktime data in accordance with the next state.

In yet another embodiment, the output clock generating device (5)includes a prescribed number (N) of multipliers that multiply thefrequency control data and one to the prescribed number (N) of positiveinteger, respectively, a storage device configured to store data inputper clock of the one cycle, and a prescribed number (N) of adders thatadd the data stored in the storage device to outputs from the prescribednumber (N) of multipliers. An output of one of the prescribed number (N)of adders is input to the storage device, and the outputs from theprescribed number (N) of adders constitute the output clock time data.

In yet another embodiment, the phase difference detecting device (3)selects an output from one of the prescribed number (N) of adders inaccordance with the input signal time data (S2). The phase differencedetecting device (3) detects the phase difference based on the selectedoutput, and outputs the phase difference signal (S3) in accordance withthe detection result.

According to the invention of the digital phase locked loop apparatus,fine time resolution of an output clock phase is obtained whilemaintaining a frequency of an operational clock to be relatively low.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the present invention and many of theattendant advantages thereof will be readily obtained as the samebecomes better understood by reference to the following detaileddescription when considered in connection with the accompanyingdrawings, wherein:

FIG. 1 illustrates an exemplary configuration of a digital phase lockedloop circuit of a first embodiment of the present invention;

FIG. 2 illustrates exemplary operational waves appearing in the digitalphase locked loop circuit of FIG. 1;

FIG. 3 illustrates an exemplary interior configuration of an inputsignal time detection section 2 illustrated in FIG. 1;

FIG. 4 illustrates exemplary operational waves appearing in the inputsignal time detection section 2 of FIG. 3;

FIG. 5 is a block diagram illustrating an exemplary configuration of adigital phase locked loop circuit of a second embodiment according tothe present invention;

FIG. 6 is a block diagram illustrating an exemplary configuration of amulti phase clock source 6 used in the digital phase locked loop circuitof FIG. 5;

FIG. 7 is a block diagram illustrating an exemplary configuration of aninput signal time detection section 2 used in the digital phase lockedloop circuit of FIG. 5;

FIG. 8 illustrates an operational wave appearing in each of sectionsshown from FIG. 5 to FIG. 7;

FIG. 9 is a block diagram illustrating an exemplary configuration of anoutput clock generation section 5 used in a digital phase locked loopcircuit of a third embodiment according to present invention;

FIG. 10 illustrates a change of data when the output clock generationsection 5 of FIG. 9 operates;

FIG. 11 is a block diagram illustrating an exemplary configuration of anoutput clock generation section 5 used in a digital phase locked loopcircuit of a fourth embodiment according to present invention;

FIG. 12 illustrates a change of data when the output clock generationsection 5 of FIG. 11 operates;

FIG. 13 illustrates a change of data when the output clock generationsection 5 of FIG. 11 operates;

FIG. 14 illustrates a change of data when the output clock generationsection 5 of FIG. 11 operates;

FIG. 15 illustrates a change of data when the output clock generationsection 5 of FIG. 11 operates;

FIG. 16 illustrates a change of data when the output clock generationsection 5 of FIG. 11 operates;

FIG. 17 is a block diagram illustrating an exemplary configuration of anoutput clock generation section 5 used in a digital phase locked loopcircuit of a fifth embodiment according to present invention;

FIG. 18 illustrates a change of data when the output clock generationsection 5 of FIG. 17 operates;

FIG. 19 illustrates a change of data when the output clock generationsection 5 of FIG. 17 operates;

FIG. 20 illustrates a change of data when the output clock generationsection 5 of FIG. 17 operates;

FIG. 21 illustrates a change of data when the output clock generationsection 5 of FIG. 17 operates;

FIG. 22 illustrates a change of data when the output clock generationsection 5 of FIG. 17 operates;

FIG. 23 is a block diagram illustrating an exemplary configuration of aphase difference detection section 3 used in a digital phase locked loopcircuit of a sixth embodiment according to present invention;

FIG. 24 is a wave of an output signal of each of sections when the phasedifference detection section 3 of FIG. 23 operates;

FIG. 25 is a block diagram illustrating an exemplary configuration of aconventional digital phase locked loop circuit;

FIG. 26 illustrates operational waves appearing in the digital phaselocked loop circuit of FIG. 25; and

FIGS. 27 to 36 illustrate first to tenth charts, respectively, to bereferred to in relation to respective embodiments of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings, wherein like reference numerals designateidentical or corresponding parts throughout several views, in particularin FIG. 1, an exemplary configuration of a digital phase locked loopcircuit (DPLC) of a first embodiment of the present invention isillustrated. FIG. 2 illustrates operational waves appearing in thedigital phase locked loop circuit of FIG. 1. As shown in FIG. 1, a clocksource 1 provides an operational clock signal Clk1 having a cycle T1 toeach of an input signal time detection section 2, and an output clockgeneration section 5. The input signal time detection section 2 detectsa phase of an input signal S1 input to the digital phase locked loopcircuit with time resolution T2 (T2=T1/N), which is obtained by dividingthe cycle T1 of the operational clock signal Clk1 by N times. The inputsignal time detection section 2 outputs data per cycle of theoperational clock signal Clk1.

It is conditioned in the operational wave chart of FIG. 2 that theformulas T2=T1/4 and N=4 are established. The larger the N, the finerthe detection resolution in the input signal time detection section 2.However, the equality N=4 is used for the purpose of easy comprehension.As shown in FIG. 2( a), clock cycle numbers 0 to 7 are assigned torespective cycles of the operational clock signal Clk1 for explaining anoperation. As shown in FIG. 2( c), phases obtained by dividing a cycleof the operational clock signal Clk1 by N times (e.g. four) into a unitof T2 are assigned with N time division phase numbers from 4 to 1. Here,a larger N time division phase number represents an earlier time.

As shown, an input signal S1 changes from low (L) to high (H) at a timecorresponding to the N time division phase number 3 of the clock cyclenumber 0. When detecting such a changing edge, the input signal timedetection section 2 outputs the N time division phase number at the timeas input signal time data S2 during a cycle of the next operationalclock signal Clk1. As shown in FIG. 2( e), data “3” is output as aninput signal time data S2 when the clock cycle number of FIG. 2( a) is“1”. When a changing edge of the input signal S1 does not appear duringa cycle of the operational clock signal Clk1, the input signal timedetection section 2 causes input signal time data S2 output during thenext cycle of the operational clock signal Clk1 to be “0”.

Since a changing edge of the input signal S1 does not exist when theclock cycle numbers are “1” and “2” as shown in FIG. 2( a), the inputsignal time data S2 in clock cycle numbers “2” and “3” thereof becomes“0” as shown in FIG. 2( e). FIG. 3 illustrates an exemplary interiorconfiguration of an input signal time detection section 2 illustrated inFIG. 1. FIG. 4 illustrates an exemplary operational wave appearing inthe input signal time detection section 2 of FIG. 3. A gate circuit 251detects a rising edge of the operational clock signal Clk1 and outputs apulse signal S251 as shown in FIG. 4( d). A power supply source 252continuously charges a condenser 253 with a constant current. A switch254 discharges electric charge of the condenser every time when thepulse signal S251 is generated.

As a result, a signal obtained by detecting the charged voltage of thecondenser 253 via a buffer 255 comes to have the same frequency as theoperational clock signal Clk1 and forms a wave signal having a saw shape(a sawtooth wave signal) as shown in FIG. 4( f). Thus, a saw wave signalS253 as shown in (f) is output from the buffer 255.

The gate circuit 256 detects both rising and descending edges of theinput signal S1 as shown in FIG. 4( c), and outputs a pulse signal S252as shown in FIG. 4( e).

When the pulse signal S252 is generated, the switch 257 is turned on(ON), and a voltage of the saw wave signal S253 charges the condenserS252. The charged voltage is maintained until being discharged by theswitch 259 that is turned on (ON) by a pulse signal S251.

Then, a signal obtained by detecting a charged voltage of the condenser258 via a buffer 260 causes a voltage signal S254 corresponding to aphase of the generated input signal S1 as shown in FIG. 4( g). Byapplying AD conversion to the voltage signal S254 from analog to digitalusing an AD converter (ADC in the drawing) 261, input signal time dataS2 having a value corresponding to the phase of the input signal S1 canbe obtained as shown in FIG. 4( h). The output clock generation section5 changes an edge phase of a virtual output clock with time resolutionT2 in accordance with frequency control data S4. However, the virtualoutput clock is not practically output. Instead, output clock time dataS5 having a value corresponding to an edge phase of the virtual outputclock is output per cycle of the operational clock signal Clk1.

As represented by the operational waves in FIG. 2, the output clockgeneration section 5 causes the edge phase of the virtual output clockto position at the N time division phase number “2” when a clock cyclenumber of FIG. 2( a) is “0”. Data “2” is thus practically output asoutput clock time data S5 as shown in FIG. 2( i). Similarly, when theclock cycle numbers of FIG. 2( a) are 1, 2, and 3, the output clockgeneration section 5 causes phases of the virtual output clock toposition at N time division phase numbers “2”, “3”, and “3”,respectively, and practically outputs data “2”, “3”, and “3” as outputclock time data S5 as shown in FIG. 2( i). An edge of a virtual outputclock is not generated during the cycle in the clock cycle number “6”.

In this situation, the output clock generation section 5 outputs data“0” as output clock time data S5. A phase difference detection section 3detects a phase difference between the input signal and the virtualoutput clock based on the input signal time data S2 and the output clocktime data S5, and outputs a phase difference signal S3 having a valuecorresponding to the detection result per cycle of the operational clocksignal Clk1. Since the phase of an input signal S1 of FIG. 2( d)corresponds to the N time division phase number “3” as shown in FIG. 2(c), and the virtual output clock phase of FIG. 2( h) corresponds to theN time division phase number “2”, the phase of the input signal S1advances by one N time division phase number from that of the virtualoutput clock when the clock cycle number of FIG. 2( a) is “0”.

The phase difference detection section 3 detects a phase differencebetween input signal time data S2 obtained in the clock cycle number “1”of FIG. 2( a) and output clock time data S5 obtained in the clock cyclenumber “0”, and outputs a phase difference signal S3 having the value“1” in the cycle of the clock cycle number “2”. When a changing edge ofthe input signal S1 or an edge of the virtual output clock does notappear during a cycle of an operational clock signal Clk1, the value ofthe phase difference signal S3 becomes “0”. The frequency controlsection 4 changes frequency control data S4 in accordance with the phasedifference signal S3. As a result, a feedback loop is formed, and thephase of the virtual output clock can synchronize with the input signalS1.

As generally known as a phase locked loop technology, the frequencycontrol section 4 generates frequency control data S4 by eithermultiplying a phase difference signal S3 and a prescribed gain orlifting a gain in a low frequency region.

Thus, the digital phase locked loop circuit of FIG. 1 can increase timeresolution of a virtual output clock phase about N times while using anoperational clock signal Clk1 having a relatively low frequency with acycle T1.

Thus, an output clock phase of fine time resolution can be providedwhile using a clock having a relatively low frequency. Because, theinput signal time detection section 2 detects a phase of an input signalS1 with time resolution T2 (T2=T1/N) calculated by dividing the cycle T1N times, and outputs input signal time data S2 having a valuecorresponding to the detection result per cycle T1. Further because, theoutput clock generation section 5 changes a phase of the virtual outputclock with time resolution T2 in accordance with frequency control data,and outputs output clock time data S5 having a value corresponding to avirtual output clock phase per cycle T1. Accordingly, fine timeresolution of an output clock phase can be realized using a relativelylow frequency operational clock.

A second exemplary embodiment is now described.

FIG. 5 is a block diagram illustrating an exemplary configuration of adigital phase locked loop circuit of a second embodiment according tothe present invention.

FIG. 6 is a block diagram illustrating an exemplary configuration of amulti phase clock source 6 used in the digital phase locked loop circuitof FIG. 5. FIG. 7 is a block diagram illustrating an exemplaryconfiguration of an input signal time detection section 2 used in thedigital phase locked loop circuit of FIG. 5. FIG. 8 illustrates anoperational wave appearing in each of sections shown in FIGS. 5 to 7.Operations of a phase difference detection section 3, a frequencycontrol section 4, an output clock generation section 5 are the same asthose illustrated in FIG. 1, thereby explanation of those are omitted.As shown in FIG. 6, a multi phase clock source 6 includes a plurality of(e.g. four) steps of differential buffers 101 to 104 serially connectedto the other while connected each of respective output buffers 105 to108.

Each of the differential buffers 101 to 104 is fed back to the firststep differential buffer 101 while an output signal of the last stepdifferential buffer 104 is reversed, thereby a ring oscillator isformed. Respective outputs of the differential buffers 101 to 104 areoutput from the differential buffers 101 to 104 via the output buffers105 to 108, respectively, as four phase operational clock signals Clk1to Clk4. These four phase operational clock signals Clk1 to Clk4 includethe same frequencies to each other and a prescribe phase difference asshown in FIGS. 8( b) to (e). Although the four differential buffers areemployed in this second example, the other number of differentialbuffers can be connected corresponding to time resolution N (positiveinteger) as necessary.

Further, although illustration is omitted in the second embodiment, adelay value of the differential buffer can be changed by changing anoperation voltage or the like of a differential buffer, accordingly,time resolution T2 can be changed. Thus, the time resolution T2 can beadjusted as necessary. As shown in FIG. 7, an input line of an inputsignal S1 is commonly connected to a D-terminal of each of four DFFs 201to 204 in an input signal time detection section 20 as a D-input.

Further, input lines of the operational clock signals Clk1 to Clk4 ofthe four different phases are connected to CK-terminals as clock signal(CK) inputs, respectively.

Further, a first combination logic 208 receives output signals of thefour DFFs 201 to 204 through respective input terminals i1 to i4,converts these output signals into two signals, and outputs those toDFFs 205 and 206 via output terminals o1 and o2, respectively.Respective output signals are input to a second combination logic 209via the DFFs 205 and 206. Output signals of the DFFs 204 and 207 arealso input to the second combination logic 209. The second combinationlogic 208 receives output signals of DFFs 205 and 206, 204, and 207through respective input terminals i1 to i2, i3, and i4, converts thesefour input signals into two output signals, and outputs input signaltime data S2.

Due to a relation between phases of the input signal S1 and the fourphase operational clock signals Clk1 to Clk4, in the input signal timedetection section 2 of FIG. 7, a combination pattern of the outputsignals of the four DFFs 201 to 204 will become different at the risingedge time of the operational clock signal Clk1. These first and secondcombination logics 208 and 209 each recognize a N time division phasenumber at a changing edge of an input signal S1 based on the combinationpattern. Operational waves are illustrated in FIGS. 8( f) to (j).Truth-values of the first and second combination logic blocks 208 and209 are illustrated in the first and second charts, respectively.

Thus, the digital phase locked loop circuit of FIG. 5 having the multiphase clock source 6 and the input signal time detection section 2 canadjust time resolutions N and T2 as necessary by controlling a number ofdifferential buffers used in the multi phase clock source 6 and anoperational voltage or the like of the differential buffer. Thus, thedigital phase locked loop circuit can increase detection time resolutionof a phase of an input signal N times while using an operational clocksignal Clk1 having a cycle T1 and a relatively low frequency. Since theinput signal time detection section 2 is entirely formed from a digitalcircuit, it is easy to be mounted on an integrated circuit, and isreadily downsized at low cost.

Thus, since the input signal time detection section 2 uses multi phaseclock signals (Clk1 to Clkn) having different phases by an amount of ascale of time resolution T2 in a cycle T1, and outputs input signal timedata S2 based on phases of the multi phase clock signals and that of theinput signal S1, the digital phase locked loop circuit can have highdetection time resolution of a phase of an input signal while using anoperational clock having a relatively low frequency, and is readilymounted on an integrated circuit. Accordingly, a digital phase lockedloop circuit readily mounted on an integrated circuit can be providedwith an input signal time detection section having high detection timeresolution of a phase of an input signal using an operational clockhaving a relatively low frequency.

A third exemplary embodiment is now described.

FIG. 9 is a block diagram illustrating an exemplary configuration of anoutput clock generation section 5 used in a digital phase locked loopcircuit of a third embodiment according to present invention. FIG. 10illustrates a change of data when the output clock generation section 5of FIG. 9 operates. According to a digital phase locked loop circuit ofthis third embodiment, number N is eight (N=8), and thereby timeresolution T2 has a time calculated by dividing a cycle T1 of anoperational clock signal Clk1 by eight. As shown in FIG. 9, the outputclock generation section 5 includes a table 501 and a DFF 502. The table501 receives an input of the frequency control data S4 and a currentstate St from the DFF 502 at input terminals Vcoln and St, respectively.The table outputs the next state StN through an output terminal StNbased on these inputs signals.

The DFF 502 latches the next state StN output from the table 501 insynchronism with a rising edge of the operational clock signal Clk1, andholds it until receiving that of the next operational clock signal Clk1.Data maintained by the DFF 502 represents a current state, and is outputby the DFF 502 as is as output clock time data S5.

The chart illustrates true value of the table 501. In the thirdembodiment, a value of the frequency control data S4 is supposed to beone of −1, 0, and +1. The third chart illustrates a value of the nextstate StN determined in accordance with a relation between the currentstate St and the frequency control data S4.

For example, when a current state St is “2” and frequency control dataS4 is “0”, the next state StN is “2” as shown on the third line in thethird chart.

The fourth chart represents a relation between a current state St, i.e.,output clock time data S5, and a phase of a virtual output clock. Asshown in the fourth chart, for example, an indication “-------” on aline on which a current state St is eight (St=8) represents that an edgeof the virtual clock exists at the “8” position among N time divisionphase numbers (8 to 1) obtained by dividing a cycle of the operationalclock signal Clk1 N times into a unit of time resolution T2. Further, anindication “-----” on a line on which the current state St is nine(St=9) represents that edges of the virtual clock exist both at thepositions of the N time division phase numbers “8” and “1”.

Further, an indication “--------” on a line on which the current stateSt is zero (St=0) represents that there is no edges of a virtual clockin a clock cycle. FIG. 10 illustrates a change of data when the outputclock generation section 5 of FIG. 9 operates for an amount of thirtythree (33) clocks (clock cycle numbers 0 to 32) with a cycle of anoperational clock signal Clk1. As shown in the drawing, since one linecan not entirely describe information, description is divided into fivelines of from (a) to (e). Among the thirty-three clocks, a value offrequency control data S4 is “−1” when clock cycle numbers are from 0 to12. The state St changes in accordance with the truth value described inthe third chart as 0, 8, 7, 6, 5, 4, 3, 2, 1, 0, and 8, and so on.

This value as is represents a virtual output clock phase. A phase of thevirtual output clock deviates backward by one N time division phasenumber per one cycle of the operational clock signal Clk1 during whenthe frequency control data S4 is “−1”. Specifically, a cycle of thevirtual output clock is calculated as 9×T2. Further, a value of thefrequency control data S4 amounts to zero and the state St maintains “5”when the clock cycle numbers are from “13 to 20”. Accordingly, an edgephase of the virtual output clock remains at the position of the N timedivision phase number “5”, and a cycle of the virtual output clock iscalculated as 8×T2.

A value of the frequency control data S4 amounts to +1 in the clockcycle numbers “21” to “32”. Further, the value of the state St changesas 5, 6, 9, 9, 2, 3, 4, 5, 6, 7, and 9, and so on

When the state St is nine (St=9), there are two virtual output clockedges.

Thus, when the frequency control data S4 is +1, a phase of the virtualoutput clock deviates forwardly by one N time division phase number percycle of the operational clock signal Clk1. Specifically, a cycle of thevirtual output clock is calculated as 7×T2. As mentioned previously, theoutput clock generation section 5 of FIG. 9 can change a cycle of thevirtual output clock in a unit of T2 serving as time resolution, whichis N times of the cycle T1 of the operational clock signal Clk1, inaccordance with a value of the frequency control data S4. Specifically,the output clock generation section 5 of FIG. 9 included in the digitalphase locked loop circuit of the third embodiment can increase timeresolution of the virtual output clock phase N times while using anoperational clock signal Clk1 having a relatively low frequency.

Thus, fine time resolution of an output clock phase can be realizedwhile using an operational clock having a relatively low frequency.Because, the output clock generation section 5 operates with a clockhaving a cycle T1 and functions as a state machine having a state(S5/St) corresponding to a virtual output clock phase. Further because,the output clock generation section 5 determines the next state StNbased on a relation between a frequency control data S4 and a currentstate St, and outputs a value corresponding to the determined state asoutput clock time data S5. Accordingly, a digital phase locked loopcircuit having an output clock generation section that generates avirtual output clock having fine time resolution phase can be realizedwhile using an operational clock having a relatively low frequency.

A fourth exemplary embodiment is now described.

FIG. 11 is a block diagram illustrating an exemplary configuration of anoutput clock generation section 5 used in a digital phase locked loopcircuit of a fourth embodiment according to present invention. FIG. 12illustrates a change of data when the output clock generation section 5of FIG. 11 operates. In a digital phase locked loop circuit of thisfourth embodiment, N is 12 (N=12), and the time resolution T2 has a timecalculated by dividing a cycle T1 of an operational clock signal Clk1 bytwelve. As shown in FIG. 11, the output clock generation section 5includes a table 511 and four DFFs 512 to 515.

The table 511 receives an input of frequency control data S4 at an inputterminal Vcoln. The table 511 also receives inputs of current statesSt0, St1, St2, St3, and St4 from the DFFs 512, 513, 514, and 515 atinput terminals St0, St1, St2, and St3, respectively. The table 511 thenoutputs the next state StN through the output terminal StN based on theinput signals from the four DFFs 512 to 515. The DFF 512 latches thenext state StN output from the table 511 in synchronism with a risingedge of the operational clock signal Clk1, and maintains it until arising edge of the next operational clock signal Clk1.

Data held by the DFF 512 represents a current state and is output fromthe DFF 512 as output clock time data S5. Since the four DFFs 512 to 515are connected in a shift register state, and the data held by the DFF512 represents current state, the following DFFs 513 to 515 hold paststates of three clocks. Specifically, the table 511 outputs the nextstate StN based on the frequency control data S4, the current state St0,and the past states St1, St2, and St3 of the three clocks. The fifthchart illustrates true-value of the table 511.

It is supposed in the fourth embodiment that a value of the frequencycontrol data S4 varies from zero to “36”. Fifth to ninth chartsillustrate values of the next states StN determined based on a relationbetween frequency data S4, the current state St, and the past statesSt1, St2, and St3. True-value practically has significantly a largevalue, the fifth to ninth charts illustrate only cases when frequencycontrol data S4 are 0, 1, 2, 35, and 36. Specifically, cases when thefrequency control data S4 are 3, 4, . . . , and 34 are omitted. Asunderstood from a regularity from the fifth to ninth charts, every timewhen frequency control data S4 increases by one, a content of the stateStN is upwardly shifted by one line. Further, the same regularityappears in the cases when the frequency control data S4 are 3, 4, . . ., and 34.

A tenth chart illustrates a relation between a current state St0, i.e.,output clock time data S5, and a virtual output clock phase. As shown inthe tenth chart, an indication “-------” on a line indicating that acurrent state St0 is twelve (St0=12) represents that there exists anedge of a virtual clock at position of the N time division phase number“12” among those “12 down to 1”, which is obtained by dividing a cycleof an operational clock signal Cklk1 by N (twelve) into a unit of timeresolution T2, for example. Further, an indication “------------” on aline indicating that the current state St0 is zero (St0=0) representsthat there exists no edges of a virtual clock in such a clock cycle.

FIGS. 12 to 14 illustrate a change of data when the output clockgeneration section 5 of FIG. 11 operates on a condition that a frequencycontrol data S4 vary from 23 to 25. As shown in the drawing, since oneline can not entirely describe information, description is divided intofive lines of from (a) to (e). As shown in FIG. 12, a state St0 changesto be 0, 12, 0, 11, 0, 10, 0, 9, 0, 8, 0, and 7, etc., in accordancewith true-value of the fifth chart when frequency control data S4 is 23(S4=23).

The value as is represents a virtual output clock phase. When frequencycontrol data S4 is twenty-three (S=23), a virtual output clock isgenerated almost once per two cycles of the operational clock signalClk1. The phase deviates afterwards by one N time division phase numberper cycle of the operational clock signal Clk1. Specifically, a cycle ofthe virtual output clock is calculated as 25×T2. As shown in FIG. 13, astate St0 changes to be 0, 12, 0, 12, 0, and 12, etc., in accordancewith the true-value of the fifth chart when frequency control data S4 is24 (S4=24).

The value as is represents a virtual output clock phase. When frequencycontrol data S4 is twenty-four (S4=24), a virtual output clock isgenerated almost once per two cycles of the operational clock signalClk1, and a phase thereof always exists at the same N time divisionphase number position.

Specifically, a cycle of the virtual output clock is calculated as24×T2. As shown in FIG. 14, a state St0 changes to be 0, 12, 1, 0, 2, 0,3, 0, 4, 0, 5, and 0, etc., in accordance with the true-value of thefifth chart when frequency control data S4 is 25 (S4=25). The value asis represents a virtual output clock phase. When frequency control dataS4 is twenty-five (S4=25), a virtual output clock is generated almostonce per two cycles of the operational clock signal Clk1, and a phasethereof deviates forward by one N time division phase number per cycleof the operational clock signal Clk1. Specifically, a cycle of thevirtual output clock is calculated as 23×T2.

FIG. 15 illustrates a change of data when the output clock generationsection 5 of FIG. 11 operates on a condition that the frequency controldata S4 is the least “0”.

FIG. 16 also illustrates a change of data when the output clockgeneration section 5 of FIG. 11 operates on a condition that thefrequency control data S4 is the maximum “36”. As shown in the drawings,since one line can not entirely describe information, description isdivided into two lines of (a) and (b). As shown in FIG. 15, a state St0changes to be 0, 12, 0, 0, 0, 12, 0, 0, 0, and 12, etc., in accordancewith the true-value of the fifth chart when the frequency control dataS4 is 0 (S4=0).

The value as is represents a virtual output clock phase. Specifically,when the frequency control data S4 is zero (S4=0), a virtual outputclock is generated almost once per four cycles of the operational clocksignal Clk1, and a phase thereof always exists at the same N timedivision phase number position. Specifically, a cycle of the virtualoutput clock is calculated as 48×T2. As shown in FIG. 16, the state St0changes to be 0, 12, 12, 12, 12, 12, and 12, etc., in accordance withthe true-value of fifth chart when the frequency control data S4 is 36(S4=36). The value as is represents a virtual output clock phase. Whenfrequency control data S4 is thirty-six (S4=36), a virtual output clockis generated almost once per cycle of the operational clock signal Clk1,and a phase thereof always exists at the same N time division phasenumber position.

Specifically, a cycle of the virtual output clock is calculated as12×T2. As mentioned heretofore, the output clock generation section 5 ofFIG. 11 can change a cycle of the virtual output clock into a unit ofT2, that realizes N times of the time resolution of the operationalclock signal Clk1 with the cycle T1, in accordance with a value offrequency control data S4. Further, an operation frequency of the outputclock widely increases from “12×T2” to “48×T2” when converted into aclock cycle in comparison with the output clock generation section 5 ofFIG. 9. Specifically, the output clock generation section 5 included inthe digital phase locked loop circuit of the fourth embodiment canincrease time resolution of a virtual output clock phase N times whileusing an operational clock signal Clk1 having a relatively lowfrequency. Further, a range of an operation frequency of the outputclock can be expanded.

Thus, the output clock generation section 5 can provide fine timeresolution of an output clock phase having a wide operation frequencyrange of an output clock while using an operational clock having arelatively low frequency. Because, the output clock generation section 5operates with a clock having a cycle T1 and functions as a state machinehaving a state (S5/St0) corresponding to a virtual output clock phase,and includes a plurality of DFFs 513 to 515 to store one or more paststates.

Further because, the output clock generation section 5 determines thenext state StN based on a relation between frequency control data S4 andone or more past states St1 to St3, and outputs a value as output clocktime data S5 corresponding to thus determined state. Accordingly, adigital phase locked loop circuit including an output clock generationsection realizing fine time resolution of an output clock phase with awide operation frequency range of an output clock can be realized whileusing an operational clock having a relatively low frequency.

A fifth exemplary embodiment is now described.

FIG. 17 is a block diagram illustrating an exemplary configuration of anoutput clock generation section 5 used in a digital phase locked loopcircuit of a fifth embodiment according to present invention. FIG. 18illustrates a change of data when the output clock generation section 5of FIG. 17 operates. In a digital phase locked loop circuit of thisillustrated embodiment, N is 8 (N=8), and accordingly time resolution T2has a time calculated by dividing the cycle T1 of the operational clocksignal Clk1 by 8. Further, frequency control data S4 ranges from 1 to 32in the fifth embodiment.

As shown in FIG. 17, the output clock generation section 5 includeseight multipliers 531 to 538 (Nos. 534 to 536 are omitted in thedrawing). These multipliers 531 to 538 multiply numbers 1 to 8 andfrequency control data S4 so as to obtain eight data of Mpy1 to Mpy8,respectively. Further, eight adders 541 to 548 (Nos. 544 to 546 areomitted in the drawing) are provided so that lower eight bit valuesFbDat among outputs of the DFF 551 can be added to the respective dataof Mpy1 to Mpy8 to obtain eight data of Add1 to Add8. A D-input to aninput terminal D of the DDF 551 is the output value Add8 of the adder548. Further, an operational clock signal Clk1 is a clock input to theinput terminal CK of the DFF 551.

Only MSB (top bit) is drawn among the data from each of the adders Add1to Add8, and is input to respective gate circuits 581 to 588. The gatecircuits 581 to 588 (Nos. 584 to 586 are omitted in the drawing))include NOT circuits 561 to 568 (Nos. 564 to 566 are omitted in thedrawing) and AND gates 571 to 578 (Nos. 574 to 576 are omitted in thedrawing), respectively. Each of outputs of the AND gates 571 to 578becomes “1” when each of the MSBs is “1” and a MSB upper by one in thedrawing is “0”. An output of the AND gate 571 becomes “1” when the MSBof the Add1 is “1” and a MSB as an output of the DFF 551 is “0”.

An 8 bit data formed by integrating the outputs of these eight AND gates571 to 578 is output as output clock time data1 (S5). In this fifthembodiment, a virtual output clock phase is represented by a bitposition where the output clock time data1 (S5) becomes “1”. FIGS. 18 to20 collectively illustrate a change of data when the output clockgeneration section 5 of FIG. 17 operates on a condition that frequencycontrol data S4 is “15”, “16”, or “17”. In each of the respectivedrawings, data of each section in the circuit is represented in one lineper cycle of an operational clock signal Clk1, wherein a line descendingdirection represents a time elapsing direction. Further, initial data ofthe DFF 551 has “64” in this embodiment.

Now, data change during an operation in the output clock generationsection 5 of FIG. 17 is partially described. For example, the eight dataMpy1, Mpy2, . . . , and Mpy8 on the line of the clock cycle number “1”in FIG. 18 become values “15”, “30”, . . . , and “120”, because, “1”,“2”, . . . , and “8” and the frequency control data “15” are multiplied.Since the value of the Add 8 is “184” in the previous clock cycle, FbDatis also “184”. The data of Add1 to Add8 become “199”, “214”, . . . , and“304” through calculation of adding FbDat to the respective eight dataof the Mpy1 to Mpy8.

MSBs of the Add1 to Add8 are extracted, respectively. A condition if aMSB is “1” and a MSB upper by one in the drawing is “0” is detected. Acondition where the Add4 is “244” (MSB=0) and Add5 is “259” (MSB=1)meets the above-mentioned condition. Thus, the fifth bit in the outputclock time data becomes “1” and represents that an edge phase of thevirtual output clock exists at this position. A smaller bit number inthe output clock time data1 illustrated in FIGS. 18 to 22 represents anearlier time in contrast to the N time division phase number asdescribed heretofore.

Specifically, it represents that when the bit number1 is “1”, an edgephase of the virtual output clock exists at the position of the N timedivision phase number “8”.

Further, when a bit number8 is “1”, an edge phase of the virtual outputclock exists at the position of the N time division phase number “1”.When frequency control data S4 is sixteen (S4=16) as illustrated in FIG.19, a virtual output clock is always generated once per two cycles ofthe operational clock signal Clk1 at the same position of the N timedivision phase number. In contrast, when frequency control data S4 isfifteen (S4=15) as illustrated in FIG. 18, a virtual output clock isgenerated almost once per two cycles of the operational clock signalClk1, and the phase gradually deviates afterwards. Specifically, afrequency of a virtual output clock decreases when the frequency controldata S4 is “15” (S4=15) than when the frequency control data S4 is “16”(S4=16).

Further, although a virtual output clock is generated almost once pertwo cycles of the operational clock signal Clk1, the phase graduallydeviates forward when the frequency control data S4 is “17” (S4=17).Specifically, a frequency of a virtual output clock is higher when thefrequency control data S4 is “17” (S4=17) than when the frequencycontrol data S4 is “16” (S4=16). FIGS. 21 and 22 illustrate a change ofdata when the output clock generation section 5 of FIG. 17 operates on acondition where frequency control data S4 is “8” or “32”. As understoodwhen the frequency control data (S4=16) is referred to, edges of virtualoutput clocks are generated in every four, two, and one cycle whenfrequency control data S4 is 8, 16, or 32, respectively.

Specifically, the output clock generation section 5 of FIG. 17 canobtain a virtual output clock frequency almost in proportion to a valueof the frequency control data S4 input thereto. Further, a gainperformance of the output clock generation section 5 of FIG. 17 isconstant, a gain of the digital phase locked loop circuit can bemaintained to be constant regardless of an operation frequency. Thus, itprovides an advantage that a pull-in time of the digital phase lockedloop circuit is stable. As mentioned heretofore, the output clockgeneration section 5 of FIG. 17 can obtain excellent gain linearity.Because, the output clock generation section 5 can increase timeresolution of a phase of a virtual output clock N-times while using anoperational clock signal Clk1 having a cycle T1 and a relatively lowerfrequency, as well as be able to expand a range of an operationfrequency of an output clock.

In other words, the output clock generation section 5 can obtain finetime resolution of a phase of an output clock while using an operationalclock having a relatively low frequency, and a wide range operationfrequency of an output clock, as well as a excellent gain linearity.Because, the output clock generation section 5 includes the N items ofthe multipliers 531 to 538 that multiply values of 1 to N and thefrequency control data S4, the DFF 551 that stores data input peroperational clock having a cycle T1 as a storage device, and the N itemsof the adders 541 to 548 that add data stored in the DFF551 to outputsfrom the N items of the multipliers 531 to 538, respectively. Furtherbecause, the DFF 55 receives an output of one adder 548 among N items ofthe adders 541 to 548 as input data thereto, and outputs output clocktime data S5 in accordance with outputs of the N items of the adders 514to 548. Accordingly, a digital phase locked loop circuit having anoutput clock generation section 5 that realizes fine time resolution ofa phase of a output clock using an operational clock having a relativelylow frequency, while having a wide range operation frequency of anoutput clock and a excellent gain linearity can be realized

A sixth exemplary embodiment is now described.

FIG. 23 is a block diagram illustrating an exemplary configuration of aphase difference detection section 3 used in a digital phase locked loopcircuit of a sixth embodiment according to present invention. FIG. 24 isa wave of an output signal of each of sections when the phase differencedetection section 3 of FIG. 23 operates.

A phase difference detection section 3 of FIG. 23 receives an input ofinput signal time data S2 and output signals Add1 to Add8 serving asoutput clock time data2 (S5) from the input signal time detectionsection 2 and the N items of adders 514 to 548 included in the outputclock generation section 5 of FIG. 17, respectively.

Each LSB (8 bit) in the Add1 to Add 8 is input to a DFF 301. The DFF 301delays input data by an amount of a cycle of an operational clock signalClk1 and outputs data DAdd1 to DAdd8, respectively. These eight delaydata DAdd1 to DAdd8 are input to a selector (SEL in the drawing) 302,and one of them is selectively output as selection data SAdd inaccordance with the input signal time data S2. A subtracter (SUB in thedrawing) 303 subtracts a value of the SAdd from fixed data “128” and isoutput as a phase difference signal S3.

As shown in FIG. 24, output clock time data2 (S5=Add1 to Add8) inputfrom the output clock generation section 5 corresponds to the operatingdata in FIG. 19. In the drawing, three cases are represented on oneoperational wave, in which a phase of an input signal S1 is differentlypositioned. Specifically, a changing edge of the input signal S1 appearsat N time division phase numbers “7”, “5”, and “2” of the clock cyclenumber “2” in these first to third cases. Similar to the data changeduring an operation as mentioned with reference to FIG. 19, an edgephase of a virtual output clock exists at positions of N time divisionphase numbers “5” of the clock cycle number “1”, and N time divisionphase numbers “5” of the clock cycle number “3” as shown in FIG. 24.

When the clock cycle number is “2” in which a change edge appears in aninput signal S1, output signals Add1 to Add8 have “80”, “96”, “112”,“128”, “144”, “160”, “176”, and “192” values, respectively. Data DAdd1to DAdd8 are delayed from these signals by one operational clock, andthese data can be obtained when the clock cycle number is “3”. Data SAddis selected from these data in accordance with a value of the inputsignal time data S2. Specifically, DAdd1 to DAdd8 are selected when theinput signal time data (S2) is “8”, “7”, . . . , and “1”, respectively.

Since S2 is eight (S2=8) in the first case, data DAdd=80 is selected.Since S2 is five (S2=5) in the second case, data DAdd=128 is selected.Since S2 is two (S2=2) in the third case, data DAdd=176 is selected.These values are subtracted from the fixed data “128”, and “+48”, “0”,and “−48” are obtained and output as a phase difference signal S3 in thefirst to third cases, respectively. In the second case, a changing edgeof the input signal S1 appears right in the middle of the former andlatter virtual clock edge phases. This situation represents that a phasedifference is nothing (0), and a phase difference signal S3 is zero. Thefirst case represents that a changing edge phase of the input signal S1is advanced from when the phase difference is nothing (0), andaccordingly, a phase difference signal S3 has a positive value.

The third case represents that a changing edge phase of the input signalS1 is delayed from the condition when the phase difference is nothing(0), and accordingly, a phase difference signal S3 has a negative value.As understood from the above-mentioned description, a difference in achanging edge phase of the input signal S1 between the first and secondcases or the second and third cases is smaller than a cycle T1 of theoperational clock Clk1 when a phase difference of the second case isnothing. Specifically, the phase difference includes only three scalesof the time resolution T2 divided N times. However, the phase differencedetection section 3 of FIG. 23 provides 48 different values in a phasedifference signal S3. Specifically, the phase difference signal S3obtained by the phase difference detection section 3 of FIG. 23 hassignificantly high phase difference detection resolution.

As mentioned heretofore, the phase difference detection section 3 ofFIG. 23 can detect a phase difference between the input signal and thevirtual output clock with high detection time resolution while using anoperational clock having a relatively low frequency. Thus, the phasedifference detection section 3 can achieve fine detection timeresolution of a phase difference between input and output signals whileusing an operational clock having a relatively low frequency. Because,the phase difference detection section 3 selects an output signal of oneof the N items of adders among output clock time data2 (S5) includingoutput signals Add1 to Add8 in accordance with input signal timedetection data S2, and detects a phase difference based on the selectionoutput value. Specifically, a digital phase locked loop circuit havingthe phase difference detection section 3 capable of detecting a phasedifference between the input and output signals with high detection timeresolution can be realized while using an operational clock having arelatively low frequency.

The phase locked loop apparatus of the present invention can also beemployed in an optical disc apparatus including a CD-drive, and a DVDdrive, as well as a magnetic disc apparatus including a MO drive.

Numerous additional modifications and variations of the presentinvention are possible in light of the above teachings. It is thereforeto be understood that within the scope of the appended claims, thepresent invention may be practiced otherwise that as specificallydescribed herein.

1. A digital phase locked loop apparatus, comprising: an input signaltime detecting device configured to detect a phase of an input signalwith prescribed time resolution obtained by dividing a cycle of anoperation clock at a prescribed time, said operation clock beinggenerated by a clock generator, said input signal time detecting deviceoutputting input signal time data in accordance with a detection resultper the cycle; an output clock generating device configured to output anoutput clock time data per the cycle in accordance with frequencycontrol data, said output clock time data having a value correspondingto a phase of a virtual output clock, said virtual output clock beinggenerated by dividing the operation clock in accordance with the timeresolution; a phase difference detecting device configured to detect adifference between phases of the input signal and the virtual outputclock, said phase difference detecting device outputting a phasedifference signal in accordance with the detection result; and afrequency control device configured to change the frequency control datain accordance with the phase difference signal.
 2. The digital phaselocked loop apparatus as claimed in claim 1, wherein said clockgenerator generates a multi phase clock including a plurality of phaseclock signals having different phases by a scale of time resolution perthe cycle.
 3. The digital phase locked loop apparatus, as claimed inclaim 1, wherein said output clock generating device is operated by aclock of the cycle and stores a state in accordance with a phase of thevirtual output clock, wherein said output clock generating devicedetermining a next state based on a relation between the frequencycontrol data and a current state, said output clock generating deviceoutputting output clock time data in accordance with the next state. 4.The digital phase locked loop apparatus, as claimed in claim 1, whereinsaid output clock generating device is operated by a clock of the cycleand including at least two storage devices configured to store a currentstate and at least one past state in accordance with a phase of thevirtual output clock, and wherein said output clock generating devicedetermining the next state based on a relation between the frequencycontrol data, a current state, and the at least one past state, saidoutput clock generating device outputting output clock time data inaccordance with the next state.
 5. The digital phase locked loopapparatus as claimed in claim 1, wherein said output clock generatingdevice includes a prescribed number of multipliers configured tomultiply the frequency control data and one to a prescribed number ofpositive integers, respectively, a storage device configured to storedata input per clock of the cycle, and a prescribed number of addersconfigured to add the data stored in the storage device to outputs fromthe prescribed number of multipliers, and wherein an output of one ofthe prescribed number of adders is input to the storage device, andwherein said outputs from the prescribed number of adders constitute theoutput clock time data.
 6. The digital phase locked loop apparatus asclaimed in claim 5, wherein said phase difference detecting deviceselects an output from one of the prescribed number of adders inaccordance with the input signal time data, said phase differencedetecting device detecting the phase difference based on the selectedoutput, and outputting the phase difference signal in accordance withthe detection result.